Generally, a liquid crystal display panel mainly comprises a Thin Film Transistor Array Substrate (TFT Array Substrate), a Color Filter (CF) substrate and a Liquid Crystal Layer located between the two substrates. The working principle is that the light of backlight module is reflected to generate images by applying driving voltages to the two glass substrate for controlling the rotations of the liquid crystal molecules in the liquid crystal layer.
To obtain more regular alignment of the liquid crystal molecules, Polyimide (PI) alignment films which have been processed with alignment treatment are arranged at sides of the Thin Film Transistor Array Substrate and Color Filter substrate close to the liquid crystal layer. In the PI alignment film processed with alignment treatment, acting forces among the branched chain group and the liquid crystal are stronger so that the liquid crystal molecules can be aligned with a certain polar angle relatively tilted to the PI alignment film surface. This certain polar angle is the pretilt angle of the liquid crystal layer. The pretilt angle can control the alignment of the liquid crystal molecules to prevent the occurrence of the antiphase domains. In some degree, it also can influence the light transmittance-voltage curve of the liquid crystal layer. A proper pretilt angle can reduce the threshold voltage and raise the liquid crystal response speed.
In the manufacture process of the liquid crystal display panel, the alignment of the PI alignment film is an important procedure. The liquid crystal molecules can be aligned in the certain direction and angle. Meanwhile, the quality of the alignment procedure will influence the view angle, the respond speed, the color expression and etc. of the liquid crystal display panel.
The alignment method of the PI alignment film mainly utilizes Rubbing as shown in FIG. 1. The method mainly utilizes a hairy roller 10 to brush a PI alignment film 50 on a glass substrate 30. With the rubbing of the hairy roller 10 to the PI alignment film 50, trenches in a certain direction are formed on the PI alignment film 50 to allow the disordered molecules in the PI alignment film 50 become aligned in a consistent direction. Accordingly, the objective of alignment is accomplished. For the liquid crystal display having different structures, the rubbing direction of the hairy roller 10 is required to amend to form different pretilt angles on the PI alignment film 50
The effect of the present rubbing alignment method relies on the quality of cloth hairs. It is highly demanded to the quality of the cloth hairs. However, no efficient method is proposed to control the quality of the cloth hairs for now. Either of the blended in particles attached on the cloth hairs, the lengths of the cloth hairs, the stretch recovery ability, rubbing force and etc. can directly affect the consistency of the trench directions. Meanwhile, if the hairy roller is not flattening, the pressing degree to the PI alignment film cannot be precisely controlled which can cause the non uniform rubbing and influence the effect of the alignment, either.
Consequently, there is a need to improve the alignment method according to prior art for promoting the stability of the alignment and promote the effect of the alignment.